1. Field of the Invention
The present invention relates to a method and an apparatus for identifying a surface of a long back-coated magnetic recording medium such as a magnetic tape to determine whether the magnetic recording medium is being properly wound around a hub or the like without being reversed or turned wrong side out as it is continuously supplied to the hub or the like.
2. Description of the Prior Art
There is known a high-density recording magnetic tape having a magnetic layer coated on one side and a back coating layer such as a carbon layer coated on the other side. Such magnetic tape, which is used for high-density recording, is manufactured in the same manner as ordinary magnetic tape. A continuous blank magnetic tape, which is about 2 to 50 times longer than commercially available magnetic tapes, is wound around a blank tape hub, and subsequently unreeled and cut to a certain length depending on the use to which it will be put. The unwound magnetic tape is wound again around a product hub before it is sold.
High-density recording magnetic tape is very thin, about 3 to 50 .mu.m thick, and hence flexible, and is also narrow, about 3 to 51 mm wide. When high-density recording magnetic tape is subjected to tension fluctuations or tortuous motions while it is being transported, the tape tends to become easily reversed or turned wrong side out. It may be wound around a product hub properly for part of its length, and then somewhere along its length become turned so that the wrong side faces out. Tension fluctuations or tortuous motions may not be strong enough to reverse a magnetic tape somewhere along its length as the tape is being wound around a product hub. However, if a blank magnetic tape is erroneously wound around a tape blank hub with the wrong side out over its entire length, then a length of tape cut from the blank tape will also be wound around a product hub with the wrong side out over the entire length thereof.
In order to prevent a magnetic tape which is wound around a product hub and has become reversed over part or all of its length from being shipped and offered for sale, as the tape is being wound around the product hub, it is necessary to inspect whether the magnetic tape is being properly wound around the product hub or has become reversed. A simple device for inspecting a tape surface applies light to the tape surface while the tape is being transported at a high speed and measures the difference between the intensity of the applied light and the intensity of the light reflected from the tape surface. Such an inspecting device is advantageous since with it the entire tape surface can be inspected quickly and simply. However, the device cannot perform stable inspection because the ratio of the intensity of the light reflected from the front of the tape to that reflected from the back of the tape is small, i.e., about 1.5, and also because the tape vibrates up and down as it is transported.
One conventional tape surface identifying device has a first detecting means which is operable when the tape is not moving and determines whether a surface (e.g., an outer surface) of a tape at each of the starting and terminal ends of the tape is the front or back of the tape, and a second detecting means which is operable when the tape is moving and continuously measures the width of the tape to check if the tape has become reversed (see Japanese Unexamined Utility Model Publication No. 57(1982)-138048). If the result of the detection carried out by either one of the first and second detecting means indicates an undesirable condition, then the tape is regarded as a defective tape.
The earlier device is disadvantageous for various reasons. Since it has two detecting means, it is large in size, costly to manufacture, and requires a complex maintenance procedure. The second detecting means cannot detect a tape reversal which occurs at a position outside its detecting range. Inasmuch as the ratio of the intensity of the light reflected from the magnetic layer to that reflected from the back coating layer of a back-coated magnetic tape is not large, it is difficult to effect accurate surface identification even when the tape is at rest. A detector which detects the intensity of the reflected light and is employed as the first detecting means, therefore, often fails to identify a tape surface properly.